A method for estimating the clamping force of a parking brake generated by an electric brake motor is discussed in DE 10 2006 052 810 A1. The electric brake motor displaces a brake piston, which carries a brake pad, and presses the brake piston against a brake disk. To be able to determine the clamping force, the current, the supply voltage of the brake motor and the engine speed are measured; subsequently, the clamping force is ascertained from a differential equation system which describes the electrical and mechanical characteristics of the brake motor.
To be able to determine the clamping force as precisely as possible, the motor constant of the electric brake motor must be known, the value of which is subject to manufacturing tolerances and may also fluctuate due to aging and temperature.